1. Field of the Invention
The present invention generally relates to multi-piece golf balls and more particularly to golf balls having at least one component made of a composition comprising a polybutadiene rubber blend. The blend includes a non-metallocene catalyzed polybutadiene rubber and a metallocene-catalyzed polybutadiene rubber. The golf ball may contain a single layered core or multi-layered core. The golf ball further includes a cover having at least one layer.
2. Brief Review of the Related Art
Today, professional and amateur golfers normally use multi-piece, solid golf balls primarily because of their playing performance properties. Such balls typically include an inner core made of a natural or synthetic rubber such as polybutadiene, styrene butadiene, or polyisoprene. The ball further includes a cover that surrounds the inner core and provides impact-durability, mechanical strength, hardness, and cut/tear-resistance to the ball. The outer cover may be made from a variety of materials including ionomer ethylene acid copolymers, polyamides, polyesters, polyurethanes, and polyureas. The ball may further include one or more intermediate layers disposed between the inner core and outer cover that may be modified to provide certain properties.
Manufacturers of golf balls use different materials to impart specific properties and features to the ball. For example, the resiliency and rebounding performance of the golf ball is based primarily on the core. The core acts as an engine for the ball. In general, the rebounding performance of the ball is based on its initial velocity after being struck by the face of the golf club and its outgoing velocity after making impact with a hard surface. More particularly, the “coefficient of restitution” or “COR” of a golf ball refers to the ratio of a ball's rebound velocity to its initial incoming velocity when the ball is fired out of an air cannon into a rigid vertical plate. The COR for a golf ball is written as a decimal value between zero and one. A golf ball may have different COR values at different initial velocities. The United States Golf Association (USGA) sets limits on the initial velocity of the ball so one objective of golf ball manufacturers is to maximize COR under these conditions. Balls with a higher rebound velocity have a higher COR value. Such golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distance.
Golf balls containing cores made of polybutadiene rubber compositions are generally known in the art. For example, Kakiuchi et al., U.S. Pat. No. 4,683,257 discloses a polybutadiene rubber composition comprising; i) a polybutadiene blend; ii) an unsaturated carboxylic acid and/or a salt thereof capable of producing crosslinking in the polybutadiene; iii) inorganic filler; and iv) organic peroxide. The polybutadiene blend includes a nickel and/or cobalt-based (non-metallocene) catalyzed polybutadiene and a lanthanide rare earth element-base catalyzed polybutadiene.
Gendreau et al., U.S. Pat. No. 4,955,613 discloses a core made from two polybutadienes, each having a Mooney viscosity of below about 50 and a cis-1,4 content of greater than about 40%. One polybutadiene is nickel- or cobalt-catalyzed (non-metallocene), while the other is lanthanide-catalyzed (non-metallocene). The golf ball product includes a mix of the two polybutadienes, a metal salt of an unsaturated carboxylic acid, and a free radical initiator to cure the composition.
Hamada et al., U.S. Pat. No. 5,082,285 discloses a core made from a rubber composition which comprises polybutadiene rubber, a crosslinking agent, and a co-crosslinking agent, wherein the polybutadiene rubber is prepared by mixing nickel-catalyzed (non-metallocene) polybutadiene rubber and cobalt-catalyzed (non-metallocene) polybutadiene rubber together.
Nesbitt, U.S. Pat. No. 6,277,920 discloses a core formed from a polybutadiene composition comprising polybutadiene, a cross-linking agent, a metal soap, and zinc oxide, wherein the polybutadiene, prior to curing of the composition, has a polydispersity of 1.9 to 3.9 and a Mooney viscosity of greater than 70. The monomer used to form the polybutadiene is polymerized in the presence of a non-metallocene catalyst, particularly cobalt, lanthanum, nickel, aluminum, boron, lithium, or titanium-based catalyst; or combinations thereof.
Binette et al., U.S. Pat. No. 6,315,684 discloses a core comprising: (i) a first polybutadiene rubber produced using a cobalt-based (non-metallocene) catalyst having a Mooney viscosity in the range of from about 70 to about 83, and (ii) a second polybutadiene rubber produced using a lanthanide series (non-metallocene) catalyst and having a Mooney viscosity of from about 30 to about 70.
Endo, U.S. Pat. No. 7,524,252 discloses a one-piece golf ball made from a polybutadiene rubber composition, wherein the composition contains 100% (parts based on total rubber) metallocene-catalyzed polybutadiene rubber. Thus, the metallocene-catalyzed polybutadiene is molded into one spherical piece to form the ball. In general, one-piece balls have several disadvantageous properties versus multi-piece golf balls including inferior playability, spin control, and flight control; and the ball tends to travel a shorter distance using driver and iron clubs. Also such one-piece balls have generally poor weatherability (they do not maintain their playing properties in hot and cold weather and have a short shelf-life and poor moisture-resistance). One-piece balls also generally have poor impact-durability; hardness, and toughness.
Sullivan, US Patent Application Publication 2012/0100934 discloses a core formed from a blend comprising a linear polybutadiene formed with a neodymium-based (non-metallocene) catalyst having a first Mooney viscosity of 30 to 100; and a branched polybutadiene formed with a neodymium-based (non-metallocene) catalyst having a second Mooney viscosity of 20 to 90. Both the linear and branched Nd-BR rubbers preferably have a cis-1,4 content of at least about 95 percent. The blend may optionally contain cobalt, lithium, titanium, or nickel catalyzed polybutadienes.
Although some conventional polybutadiene rubber compositions used to form golf ball cores today have generally good properties, there is still a need for improved polybutadiene rubber compositions. These compositions should be generally easy to manufacture, have low material costs, and provide the finished golf ball with optimum playing performance properties. Particularly, the polybutadiene rubber composition should be capable of providing a core having high resiliency so that a player can drive the ball long distances. The core material also should have good durability and toughness. The present invention provides such core compositions and resulting golf balls having these properties as well as other advantageous characteristics, features, and benefits.